[Elecraft] K3 rtty decode vs: computer decode

[Jim Brown]

On 3/24/2014 5:30 PM, Fred Jensen wrote:
> Even cheap sound cards deliver essentially pure sine wave audio, 

Not quite.  I've measured audio distortion at -30dB re: carrier for a 
reasonably OK laptop sound card just below clip. That means you have 
spurs only 30 dB below your signal. Not very good. Distortion (and thus 
those sidebands) drops by 10 dB re: carrier if you reduce the output 
level by 6 dB (half the voltage). My measurements are of the audio 
coming out of the sound card.

But I do agree that carefully generated AFSK is just fine, and that's 
what I've always done.

73, Jim K9YC